1. Field of the Invention
The present invention is directed to a method for the operation of an ultrasound therapy apparatus of the type, wherein a high-frequency generator generates an electrical signal that is time-variable in frequency, and the signal is supplied via a transmission amplifier to an ultrasound transducer arrangement.
The invention is also directed to an ultrasound therapy apparatus of the type having a high-frequency generator that is connected to an ultrasound transducer arrangement via a transmission amplifier.
2. Description of the Prior Art
In order to avoid skin burns, local acoustic field elevations in the application region are neutralized by wobbling the therapy frequency within a frequency band, as disclosed in the German OS 43 11 327. The therapy frequency is steadily varied between an upper and lower limit frequency, so that secondary maxima in the acoustic field are steadily spatially displaced. Given longer application at a constant location, the secondary maxima cause skin burns. European Application 0 534 607 discloses an apparatus wherein heat therapy of tumors can be implemented with focused ultrasound within a magnetic resonance apparatus.
When a diagnostic magnetic resonance apparatus is operated simultaneously with an ultrasound therapy apparatus, for example for monitoring the progress of the therapy, the operation of the ultrasound therapy apparatus leads to disturbances in the magnetic resonance image because harmonics of the therapy frequency couple into the high-frequency reception channel. Fast magnetic resonance sequences with a reception bandwidth of up to .+-.200 kHz are particularly very sensitive with respect to noise emissions. Only a non-simultaneous operation of the ultrasound therapy apparatus with the magnetic resonance apparatus is then possible. Therapy monitoring with the magnetic resonance apparatus thus is greatly restricted.